Embodiments of the invention relate to a semiconductor device and a method for manufacturing semiconductor device.
As the process technology for microfabrication of semiconductor devices has been rapidly developed, a technique of isolating a device region from other regions of a wafer is considered as one of the most important techniques. A so-called local oxidation of silicon (LOCOS) technique for forming device isolation layers by selectively growing a thick oxidation layer on a substrate is widely used as a device isolation technique.
The LOCOS technique has a significant disadvantage in that the width of a device isolation region cannot be reduced to below a certain level due to lateral diffusion of a device isolation region (e.g., lateral oxide growth) and formation of a bird's beak. Therefore, alternative techniques such as trench formation and shallow trench isolation (STI) techniques have been recently used.
A device isolation region formed by the STI technique includes an oxide layer for amending or repairing damaged silicon at an etched surface of the trench. However, since the oxide layer has a single-layer structure, a situation where leakage current increases due to high-speed operation of an active device in an active region of the substrate cannot be flexibly handled. This deteriorates the isolating and/or insulating ability of the device isolation region and may make it difficult to increase electron mobility in the device formed in the active region.